Steel trusses make up the framing of a building before all other walls, floors, and ceilings are installed. Typical trusses for smaller buildings or homes are normally made from wood.
The advantages of steel trusses include being lightweight and mold resistant, unlike wood framing. Also, steel material makes it possible to span a large area, such as an airplane hangar. Perhaps the most important advantage is the fact that steel is not combustible like wood, making it resilient in a fire.
The fact that steel is non-combustible allows a steel structure to negate the need for some sprinkler assemblies or other fire water systems deemed necessary by fire marshals.